Designation D6001 − 05 (Reapproved 2012) Standard Guide for Direct Push Groundwater Sampling for Environmental Site Characterization1 This standard is issued under the fixed designation D6001; the num[.]
Trang 1Designation: D6001−05 (Reapproved 2012)
Standard Guide for
Direct-Push Groundwater Sampling for Environmental Site
This standard is issued under the fixed designation D6001; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision A number in parentheses indicates the year of last reapproval A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1 Scope
1.1 This guide covers a review of methods for sampling
groundwater at discrete points or in increments by insertion of
sampling devices by static force or impact without drilling and
removal of cuttings By directly pushing the sampler, the soil is
displaced and helps to form an annular seal above the sampling
zone Direct-push water sampling can be one time, or multiple
sampling events Methods for obtaining water samples for
water quality analysis and detection of contaminants are
presented
1.2 Direct-push methods of water sampling are used for
groundwater quality studies Water quality may vary at
differ-ent depths below the surface depending on geohydrologic
conditions Incremental sampling or sampling at discrete
depths is used to determine the distribution of contaminants
and to more completely characterize geohydrologic
environ-ments These investigations are frequently required in
charac-terization of hazardous and toxic waste sites
1.3 Direct-push methods can provide accurate information
on the distribution of water quality if provisions are made to
ensure that cross-contamination or linkage between water
bearing strata are not made Discrete point sampling with a
sealed (protected) screen sampler, combined with on-site
analysis of water samples, can provide the most accurate
depiction of water quality conditions at the time of sampling
Direct-push water sampling with exposed-screen sampling
devices may be useful and are considered as screening tools
depending on precautions taken during testing Exposed screen
samplers may require development or purging depending on
sampling and quality assurance plans Results from direct-push
investigations can be used to guide placement of permanent
groundwater monitoring wells and direct remediation efforts
Multiple sampling events can be performed to depict
condi-tions over time Use of double tube tooling, where the outer
push tube seals the hole, prevents the sampling tools from coming in contact with the formation, except at the sampling point
1.4 Field test methods described in this guide include installation of temporary well points, and insertion of water samplers using a variety of insertion methods Insertion
meth-ods include: (1) soil probing using combinations of impact,
percussion, or vibratory driving with or without additions of
smooth static force; (2) smooth static force from the surface
using hydraulic cone penetrometer (Guide D6067) or drilling equipment (Guide D6286), and incremental drilling combined with direct-push water sampling events Under typical incre-mental drilling operations, samplers are advanced with assis-tance of drilling equipment by smooth hydraulic push, or mechanical impacts from hammers or other vibratory equip-ment Direct-push water sampling maybe combined with other sampling methods (Guide D6169) in drilled holes Methods for borehole abandonment by grouting are also addressed 1.5 Direct-push water sampling is limited to soils that can
be penetrated with available equipment In strong soils damage may result during insertion of the sampler from rod bending or assembly buckling Penetration may be limited, or damage to samplers or rods can occur in certain ground conditions, some
of which are discussed in5.6 Information in this procedure is limited to sampling of saturated soils in perched or saturated groundwater conditions Some soil formations do not yield water in a timely fashion for direct-push sampling In the case
of unyielding formations direct-push soil sampling can be performed (Guide D6282)
1.6 This guide does not address installation of permanent water sampling systems such as those presented in Practice
D5092 Direct-push monitoring wells for long term monitoring are addressed in Guide D6724and PracticeD6725
1.7 Direct-push water sampling for geoenvironmental ex-ploration will often involve safety planning, administration, and documentation
1.8 This guide does not purport to address all aspects of exploration and site safety It is the responsibility of the user of this guide to establish appropriate safety and health practices and determine the applicability of regulatory limitations before its use.
1 This guide is under the jurisdiction of ASTM Committee D18 on Soil and Rock
and is the direct responsibility of Subcommittee D18.21 on Groundwater and
Vadose Zone Investigations.
Current edition approved Jan 15, 2012 Published December 2012 Originally
approved in 1996 Last previous edition approved in 2005 as D6001 – 05 DOI:
10.1520/D6001-05R12.
Trang 21.9 This guide offers an organized collection of information
or a series of options and does not recommend a specific
course of action This document cannot replace education or
experience and should be used in conjunction with professional
judgment Not all aspects of this guide may be applicable in all
circumstances This ASTM standard is not intended to
repre-sent or replace the standard of care by which the adequacy of
a given professional service must be judged, nor should this
document be applied without consideration of a project’s many
unique aspects The word “Standard” in the title of this
document means only that the document has been approved
through the ASTM consensus process.
2 Referenced Documents
2.1 ASTM Standards:2
D653Terminology Relating to Soil, Rock, and Contained
Fluids
D2488Practice for Description and Identification of Soils
(Visual-Manual Procedure)
D4448Guide for Sampling Ground-Water Monitoring Wells
D4750Test Method for Determining Subsurface Liquid
Levels in a Borehole or Monitoring Well (Observation
Well)(Withdrawn 2010)3
D5088Practice for Decontamination of Field Equipment
Used at Waste Sites
D5092Practice for Design and Installation of Groundwater
Monitoring Wells
D5254Practice for Minimum Set of Data Elements to
Identify a Ground-Water Site
D5314Guide for Soil Gas Monitoring in the Vadose Zone
D5434Guide for Field Logging of Subsurface Explorations
of Soil and Rock
D5474Guide for Selection of Data Elements for
Groundwa-ter Investigations
D5521Guide for Development of Groundwater Monitoring
Wells in Granular Aquifers
D5730Guide for Site Characterization for Environmental
Purposes With Emphasis on Soil, Rock, the Vadose Zone
and Groundwater(Withdrawn 2013)3
D5778Test Method for Electronic Friction Cone and
Piezo-cone Penetration Testing of Soils
D5903Guide for Planning and Preparing for a Groundwater
Sampling Event
D6067Practice for Using the Electronic Piezocone
Pen-etrometer Tests for Environmental Site Characterization
D6089Guide for Documenting a Groundwater Sampling
Event
D6235Practice for Expedited Site Characterization of
Va-dose Zone and Groundwater Contamination at Hazardous
Waste Contaminated Sites
D6452Guide for Purging Methods for Wells Used for
Groundwater Quality Investigations
D6517Guide for Field Preservation of Groundwater Samples
D6564Guide for Field Filtration of Groundwater Samples D6634Guide for Selection of Purging and Sampling De-vices for Groundwater Monitoring Wells
D6724Guide for Installation of Direct Push Groundwater Monitoring Wells
D6725Practice for Direct Push Installation of Prepacked Screen Monitoring Wells in Unconsolidated Aquifers D6771Practice for Low-Flow Purging and Sampling for Wells and Devices Used for Ground-Water Quality Inves-tigations(Withdrawn 2011)3
D6911Guide for Packaging and Shipping Environmental Samples for Laboratory Analysis
2.2 Drilling Methods:2
D5781Guide for the Use of Dual-Wall Reverse-Circulation Drilling for Geoenvironmental Exploration and the Instal-lation of Subsurface Water-Quality Monitoring Devices D5782Guide for the Use of Direct Air-Rotary Drilling for Geoenvironmental Exploration and the Installation of Subsurface Water-Quality Monitoring Devices
D5783Guide for the Use of Direct Rotary Drilling with Water-Based Drilling Fluid for Geoenvironmental Explo-ration and the Installation of Subsurface Water-Quality Monitoring Devices
D5784Guide for the Use of Hollow-Stem Augers for Geoenvironmental Exploration and the Installation of Subsurface Water-Quality Monitoring Devices
D5875Guide for the Use of Cable-Tool Drilling and Sam-pling Methods for Geoenvironmental Explorations and Installation of Subsurface Water-Quality Monitoring De-vices
D5876Guide for the Use of Direct Rotary Wireline Casing Advancement Drilling Methods for Geoenvironmental Exploration and the Installation of Subsurface Water-Quality Monitoring Devices
D6286Guide to the Selection of Drilling Methods for Environmental Site Characterization
2.3 Soil Sampling:2
D4700Guide for Soil Sampling from the Vadose Zone D6169Guide to the Selection of Soil and Rock Sampling Devices Used With Drilling Rigs for Environmental Investigations
D6282Guide for Direct-Push Soil Sampling for Environ-mental Site Characterization
3 Terminology
3.1 Terminology used within this guide is in accordance with Terminology D653with the addition of the following:
3.2 Definitions in Accordance with Practice D5092: 3.2.1 bailer—a hollow tubular receptacle used to facilitate
removal of fluid from a well or borehole
3.2.2 borehole—a circular open or uncased subsurface hole
created by drilling
3.2.3 casing—pipe, finished in sections with either threaded
connections or beveled edges to be field welded, which is installed temporarily or permanently to counteract caving, to
2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 The last approved version of this historical standard is referenced on
www.astm.org.
Trang 3advance the borehole, or to isolate the interval being
monitored, or combination thereof
3.2.4 caving; sloughing—the inflow of unconsolidated
ma-terial into a borehole that occurs when the borehole walls lose
their cohesive strength
3.2.5 centralizer—a device that helps in the centering of a
casing or riser within a borehole or another casing
3.2.6 jetting—when applied as a drilling method, water is
forced down through the drill rods or riser pipe and out through
the end openings The jetting water then transports the
gener-ated cuttings to the ground surface in the annulus of the drill
rods or casing and the borehole The term jetting may also refer
to a well development technique
3.2.7 PTFE tape—joint sealing tape composed of
polytetra-fluorethylene
3.2.8 well screen—a filtering device used to retain the
primary or natural filter pack; usually a cylindrical pipe with
openings of uniform width, orientation, and spacing
3.3 Definitions of Terms Specific to This Standard:
3.3.1 assembly length—length of sampler body and riser
pipes
3.3.2 bentonite—the common name for drilling fluid
addi-tives and well construction products consisting mostly of
naturally occurring sodium montmorillonite Some bentonite
products have chemical additives that may affect water quality
analyses (see9.3.3)
3.3.3 direct-push sampling—sampling devices that are
di-rectly inserted into the soil to be sampled without drilling or
borehole excavation
3.3.4 drill hole—a cylindrical hole advanced into the
sub-surface by mechanical means; also, known as borehole or
boring
3.3.5 effective screen length—the length of a screen open or
exposed to water bearing strata
3.3.6 effective seal length—the length of soil above the well
screen that is in intimate contact with the riser pipe and
prevents connection of the well screen with groundwater from
other zones
3.3.7 grab sampling—the process of collecting a sample of
fluid exposed to atmospheric pressure through the riser pipe
with bailers or other methods that may include pumping; also
known as batch sampling
3.3.8 incremental drilling and sampling—insertion method
where rotary drilling and sampling events are alternated for
incremental sampling Incremental drilling is often needed to
penetrate harder or deeper formations
3.3.9 percussion driving—insertion method where rapid
hammer impacts are performed to insert the sampling device
The percussion is normally accompanied with application of
static down force
3.3.10 push depth—the depth below a ground surface datum
that the end or tip of the direct-push water sampling device is
inserted
4 Summary of Guide
4.1 Direct-push water sampling consists of pushing a pro-tected well screen to a known depth, opening the well screen over a known interval, and sampling water from the interval A well point with an exposed screen can also be pushed with understanding of potential cross-contamination effects and purging requirements considered A sampler with constant outside diameter is inserted directly into the soil by hydraulic jacking or hammering until sufficient riser pipe is seated into the soil to ensure a seal Protected well screens can be exposed
by retraction of riser pipes While the riser is seated in the soil, water samples can be taken, and water injection or pressure measurements may be performed
5 Significance and Use
5.1 Direct-push water sampling is an economical method for obtaining discrete groundwater samples without the
ex-pense of permanent monitoring well installation ( 1-6 ).4This guide can be used to profile potential groundwater contamina-tion with depth by performing repetitive sampling events Direct-push water sampling is often used in expedited site characterization (PracticeD6235) Soils to be sampled must be permeable to allow filling of the sampler in a relatively short time The zone to be sampled can be isolated by matching well screen length to obtain discrete samples of thin aquifers Use of these sampling techniques will result in more detailed charac-terization of sites containing multiple aquifers By inserting a protected sampling screen in direct contact with soil and with watertight risers, initial well development (Guide D5521) and purging of wells (Guide D6452) may not be required for the first sampling event Discrete water sampling, combined with knowledge of location and thickness of target aquifers, may better define conditions in thin multiple aquifers than monitor-ing wells with screened intervals that can intersect and allow
for intercommunication of multiple aquifers ( 4 , 6 , 7 , 8 , 9 )
Direct-push sampling performed without knowledge of the location and thickness of target aquifers can result in sampling of the wrong aquifer or penetration through confining beds
5.2 For sites that allow surface push of the sampling device, discrete water sampling is often performed in conjunction with the cone penetration test (Test MethodD6067) ( 4-8 ), which is
often used for stratigraphic mapping of aquifers, and to delineate high-permeability zones In such cases, direct-push water sampling is normally performed close to cone holes In complex alluvial environments, thin aquifers may vary in continuity such that water sampling devices may not intersect the same layer at equivalent depths as companion cone penetrometer holes
5.3 Water sampling chambers may be sealed to maintain in situ pressures and to allow for pressure measurements and
permeability testing ( 6 , 8 , 11 ) Sealing of samples under
pres-sure may reduce the possible volatilization of some organic compounds Field comparisons may be used to evaluate any systematic errors in sampling equipments and methods Com-parison studies may include the need for pressurizing samples,
4 The boldface numbers in parentheses refer to a list of references at the end of this guide.
Trang 4or the use of vacuum to extract fluids more rapidly from low
hydraulic conductivity soils (8.1.5.3)
5.4 Degradation of water samples during handling and
transport can be reduced if discrete water sampling events with
protected screen samplers are combined with real time field
analysis of potential contaminants In limited studies,
research-ers have found that the combination of discrete protected
screen sampling with onsite field analytical testing provide
accurate data of aquifer water quality conditions at the time of
testing ( 4 , 6 ) Direct-push water sampling with exposed screen
sampling devices, which may require development or purging,
are considered as screening tools depending on precautions that
are taken during testing
5.5 A well screen may be pushed into undisturbed soils at
the base of a drill hole and backfilled to make permanent
installed monitoring wells Procedures to complete direct-push
wells as permanent installations are given in Practice D6725
and Guide D6724
5.6 In difficult driving conditions, penetrating to the
re-quired depth to ensure sealing of the sampler well screen may
not be possible If the well screen cannot be inserted into the
soil with an adequate seal, the water-sampling event would
require sealing in accordance with Practice D5092 to isolate
the required aquifer Selection of the appropriate equipment
and methods to reach required depth at the site of concern
should be made in consultation with experienced operators or
manufacturers If there is no information as to the subsurface
conditions, initial explorations consisting of
penetration-resistance tests, such as Test Method D6067, or actual
direct-push testing trials can be performed to select the appropriate
testing system
5.6.1 Typical penetration depths for a specific equipment
configuration depend on many variables Some of the variables
are the driving system, the diameter of the sampler and riser
pipes, and the resistance of the materials
5.6.2 Certain subsurface conditions may prevent sampler
insertion Penetration is not possible in hard rock and usually
not possible in softer rocks such as claystones and shales
Coarse particles such as gravels, cobbles, and boulders may be
difficult to penetrate or cause damage to the sampler or riser
pipes Cemented soil zones may be difficult to penetrate
depending on the strength and thickness of the layers If layers
are present that prevent direct-push from the surface, the rotary
or percussion drilling methods (Guide D6286) can be
em-ployed to advance a boring through impeding layers to reach
testing zones
5.6.3 Driving systems are generally selected based on
re-quired testing depths and the materials to be penetrated For
systems using primarily static reaction force to insert the
sampler, depth will be limited by the reaction weight of the
equipment and penetration resistance of the material The
ability to pull back the rod string is also a consideration Impact
or percussion soil probing has an advantage of reducing the
reaction weight required for penetration Penetration capability
in clays may be increased by reducing rod friction by enlarging
tips or friction reducers However, over reaming of the hole
may increase the possibility of rod buckling and may allow for
communication of differing groundwater tables Hand-held equipment is generally used on very shallow investigations, typically less than 5-m depth, but depths on the order of 10 m have been reached in very soft lacustrine clays Intermediate size driving systems, such as small truck-mounted hydraulic-powered push and impact drivers, typically work within depth ranges from 5 to 30 m Heavy static-push cone penetrometer vehicles, such as 20-ton trucks, typically work within depth ranges from 15 to 45 m, and also reach depth ranges on the order of 102 m in soft ground conditions Drilling methods (Guide D6286) using drilling and incremental sampling are frequently used in all depth ranges and can be used to reach depths on the order of 103 m
N OTE 1—Users and manufacturers cannot agree on depth ranges for different soil types Users should consult with experienced producers and manufacturers to determine depth capability for their site conditions.
5.7 Combining multiple-sampling events in a single-sample chamber without decontamination (PracticesD5088) is gener-ally unacceptable In this application, purging of the chamber should be performed to ensure isolation of the sampling event Purging should be performed by removing several volumes of fluid until new chemical properties have been stabilized or elements are flushed with fluid of known chemistry Purging requirements may depend upon the materials used in the sampler and the sampler design (Guide D6634)
6 Apparatus
6.1 General—A direct-push sampling system consists of a
tip; well screen; chambers, if present; and riser pipes extending
to the surface Direct-push water sampling equipment can be grouped into two classes, either with a sealed protected screen
or exposed screen (see6.2) There are also two types of drive systems, single tube and double tube (see6.4)
6.2 Samplers with sealed screens depend on the seal to avoid exposure of the sampling interval to soil or water from other layers They can be considered as accurate point-source detectors They are normally decontaminated between sam-pling events Exposed-screen samplers may require purging and development and as such are considered as screening devices for profiling relative degrees of contamination
6.2.1 Exposed-Screen Samplers—Some direct-push
sam-plers may consist of a simple exposed well screen and riser pipe that allows grab sampling with bailers or pumps An example of this arrangement is the simple push or well point shown inFig 1( 12 ) The practice of jetting well points is often
not acceptable due to the large quantities of water used for insertion and the resulting potential for disturbance and dilu-tion in the aquifer If water is used for inserdilu-tion, knowing the chemical constituents in the water may be necessary Bias may
be possible if an exposed-screen sampler is pushed through multiple contaminated layers If exposed-screen well points are pushed through predrilled holes the screen and riser may fill with water present in the drill hole and require purging before sampling One form of exposed screen sampler has been developed for multiple sampling events as an exposed tip is
advanced ( 13 , 14 ) This multiple event “groundwater profiler”
injects distilled water out of the ports in between sampling
Trang 5events which keep the port from clogging and purges the
sampling line between sampling events
6.2.1.1 Another form of an exposed-screen sampler has
been incorporated into cone penetrometer bodies ( 10 ) The
cone penetrometers have sample chambers with measurement
devices such as temperature and conductivity Some cone
penetrometers have been equipped with pumps for drawing in
water samples into sample chambers or to the surface
Sam-plers equipped with chambers and subjected to multiple
sampling events may require purging between sampling
events
6.2.2 Sealed-Screen Samplers—Protected well screen and
simple riser pipes for grab sampling are also deployed An
example is shown in Fig 2 ( 15 ) This simple well screen
arrangement allows for grab sampling through the riser pipe without purging or development if there is no leakage at the screen seals and riser pipes Fig 3 shows a schematic of a direct-push water sampler with a protected screen and with the ability to work in the grab sampling mode or by allowing water
to enter a sample chamber in the sampler body ( 5 ) Most
simple sample chambers allow for flow through the chamber When flow through chambered samplers is opened, it is possible that the groundwater from the test interval can fill into the rods above the chamber In those cases, it may be advisable
to add water of known chemistry into the rods prior to opening the screen Some protected-screen samplers have sample chambers designed to reduce volume and pressure changes in the sample to avoid possible volatilization of volatile
com-pounds ( 6 , 8 , 11 ) The need for pressurization is dependent on
the requirements of the investigation program and should be evaluated by comparison studies in the field with simpler systems allowing the sample to equalize at atmospheric pres-sure There are different approaches to pressurizing the sample chamber including use of inert gas pressure or using sealed systems An example of a sealed vial-septum system is shown
inFig 4( 6 ) In the sealed vial system, a septum is punctured
with a hypodermic needle connected to a sealed vial With this approach the vial will contain both a liquid and gas at aquifer pressure The sealed vial-septum system has been used in an exposed-screen mode
6.2.3 Materials of Manufacture—The choice of materials
used in the construction of direct-push water sampling devices should be based on the knowledge of the geochemical envi-ronment to be sampled and how the materials may interact with the sample by means of physical, chemical, or biological processes Due to the nature of insertion of these devices, the sampler body is typically comprised of steel, stainless steel, or metals of other alloys The type of metal should be selected based on possible interaction effects with the fluid to be sampled Well-screen materials can be selected from a variety
of materials Materials commonly used for well-screen ele-ments include steel, stainless steel, rigid polyvinyl chloride (PVC), polytetrafluorethylene (PTFE), polyethylene (PE), polypropylene (PP), and brass Sample chambers, pumps, and connector lines are also constructed with a variety of materials Evaluating the possible interaction of materials that will be exposed to the water during the sampling event is important
6.3 Sampler Body—The sampler body consists of a tip, and
a barrel that consists of well screen, a protective sleeve if used, and a sampling chamber if used, with a connector assembly to attach to riser pipes or tubing The sampler is normally constructed of steel to withstand insertion forces The sampler barrel should be of constant outside diameter to ensure intimate contact with the soil to be tested Protective sleeves shall be equipped with O-rings to prevent the ingress of water before the sampling event
6.3.1 Expendable Sampler Tips—Some sampler tips are
expendable and are left in the ground after the sampling event The tip should be equipped with an O-ring seal to the sampler sleeve to prevent leakage into the riser pipe until the sampling depth is reached
FIG 1 Exposed-Screen Sampler—Well Point Driven Below the
Base of a Borehole ( 11 )
Trang 66.3.1.1 Sampler tips are designed so that upon pull back of
the sampler body and riser pipe, the tip is disconnected from
the sampler The required diameter, and the ability to expend
the tip successfully, depends on the soils to be penetrated The
tip diameter can be set equal to, or slightly less than, the
sampler body If there are problems with tip retraction, tips can
be designed with a diameter of 1 to 3 mm (1⁄8to1⁄16in.) larger
than the sampler body The use of an enlarged diameter with a
larger shoulder or tip may help in reaching greater depths
because it acts as a friction reducer An enlarged tip should not
leave too large an annulus above the sampler body and riser
pipes as to maintain a seal above the well screen and to prevent
potential cross contamination
6.3.1.2 Most sampler tips are made of steel to withstand
pushing forces With some samplers, after the sampling event,
the tip may remain in the ground and the hole may be grouted
The user should consider if leaving the tips below the ground
will adversely affect surrounding groundwater chemistry de-pending on site conditions
6.3.2 Well Screen—Many materials for well screens are
available for direct-push samplers The material of manufac-ture should be selected with consideration of chemical com-position of the groundwater to be sampled and possible interactive effects (see 6.2.3) Some samplers use simple mill slotted steel, or PVC tube Steel or brass screen formed into a cylinder can be used to cover inlets Continuous-wrapped, wire-wound well points are also commonly used The effective opening size of the well screen material should be selected based on the material to be sampled, the time required to sample, and soil sediment that can be tolerated in the water sample Methods to size well-screen and filter-pack materials are given in Practice D5092 Clean sands and gravels can be sampled with a screen with larger openings without producing excessive sediment Clayey and silty soils containing fines may
The assembled Sampler is driven to the desired sampling depth using standard rods.
Extension rods are used to hold the screen in position as the Cas-ing Puller Assembly is used to retract the rods.
The tubing check valve can be used to sample groundwater.
Abandonment grout-ing can be conducted
to meet ASTM re-quirements.
FIG 2 Simple Protected Screen Sampler ( 9 )
Trang 7require finer openings Typical openings of 10 to 60 µm are
used Finer openings will reduce sediment but may also slow
ingress of fluid
6.3.3 Some sampler inlets are not protected by well screen
or slotting The simplest form of sampler can be an open riser
pipe with an expendable tip The use of unprotected inlets has
sometimes been useful to sample groundwater at soil/bedrock
interface If unprotected inlets are used, one must consider the
amount of soil sediment that can be tolerated in the sample
6.4 Push Rod, Single Tube and Double Tube Systems and
Riser Pipes—Also commonly referred to as “push rods” or
“extension rods,” drive tubes are normally constructed of steel
to withstand pushing and impactforces Most double tube
systems use an outer casing and inner drive rods The inner
drive rods are removed when ready for sampling (Fig 5) Double-tube systems are advantageous if multiple sampling events are required in a single push The outer casing of a double tube system prevents cross contamination from differ-ent aquifers Some systems may use a double-tube system with
a small-diameter PVC riser pushed by the steel tube (Fig 6)
( 12 ) Other temporary systems may use a flexible tubing
system connected to the well point (Fig 7) ( 12 ) Most double
tube systems have larger outside diameter and required more driving power Single rod systems (Fig 2) sometime have a larger diameter sampling body in front of smaller diameter drive rods and can cause concern if the sampler has to be driven through multiple aquifers The single rod system is generally used for one time sampling events in the same hole
Legend: Grab Sampling Legend: Water Sampling in Chamber
A Penetrometer closed while being driven into position A Penetrometer closed while being driven into position.
B Tool opened and 5 foot screen telescopes into position for
collec-tion of hydrocarbon or water sample at the very top of the aquifer.
B Cone separated and tool open to collect sample.
C Hydrocarbon sample being collected using bailer lowered through
drive casing.
C Check valves closed as sample is retrieved within body of the tool.
FIG 3 Protected Screen Sampler Capable of Working in Grab or Chamber Sampling Modes ( 1 )
Trang 8The maximum rod diameter that can be used depends on the
material to be penetrated and the driving system Increased rod
diameter causes increase in the required driving force required
to penetrate a sufficient distance Most surface direct-push riser
pipes are less than 50 mm (2 in.) in diameter
6.4.1 Cone penetrometer rods as specified in Test Method
D5778are sometimes used in sampling systems deployed with
cone penetrometer equipment Larger diameter rods, typically
45 mm (1.75 in.), are sometimes used with cone penetrometer
equipment
6.4.2 Standard drilling rods used for rotary drilling are
normally used when sampling is done at the base of drill holes
Many drill rods are available (see Guide D6286)
6.4.3 For direct-push sampling systems that depend on the
riser pipe for sampling within the riser, ensuring that joints are
watertight will be necessary such that water enters through the
well screen interval to be sampled Rods should be
wrench-tightened, and PFTE tape can be used on the threads to stop
leakage The quality checks discussed in Section 8 can be
performed to evaluate possible leakage Sometimes it may be
necessary to equip rod joint shoulders with O-rings to prevent
leakage Cone penetrometer rods with precision tapered threads are normally watertight during short sampling events lasting up to 1 h if they are not damaged
6.4.4 Friction Reducers—Friction reducers that have
en-larged outside diameters of the riser pipe are sometimes employed to reduce thrust capacity needed to advance the well point or sampler If friction reducers are used, they must be a sufficient distance above the sampling location to ensure that fluids from overlying layers cannot enter the sampling zone If cross-contamination is possible, use of friction reducers should
be avoided In some cases the use of friction reducers can help
in forming an annular seal Donut-type reducers ream the hole smoothly Lug-type reducers rip and remold the soil and may provide a better annular seal The type and location of friction reducers should be documented in the project report
6.4.5 Mud Injection—Some direct-push systems inject
ben-tonite drill fluid along the drill rods to reduce friction These systems normally inject the fluid behind friction reducers These systems may provide better sealing above the sampler for the sampling process but are also more difficult to operate
Closed Position Open Position Sample Collection
Configuration
FIG 4 Protected Screen Sampler with Sealed Vial System ( 4 )
Trang 96.5 Sampling Devices—Consult GuideD6634for selection
of sampling devices Due to the small diameter of most
direct-push equipment, pump selection is limited Bladder
pumps, gas-displacement pumps, peristaltic pumps, and
iner-tial lift (tubing check valve) pumps may all be used for
sampling
6.6 Sample Containers—Sample containers for sampling
groundwater are addressed in GuideD6911
6.7 Driving or Pushing Equipment—Soil probing
(percus-sion driving) systems, penetrometer systems, and rotary drill-ing equipment are used for insertdrill-ing direct-push water sam-pling devices The equipment should be capable of applying sufficient mechanical force or have sufficient reaction weight,
or both, to advance the sampler or screen to a sufficient depth
to ensure an effective seal above the area to be sampled The advancement system must also have sufficient retraction force
FIG 5 Double Tube Sealed Screen Sampler
Trang 10to remove the rods, which is often a more difficult task than
advancing the rods Simple advancement systems include
hand-held rotary-impact hammers with mechanical-extraction
jacks Many systems use hydraulic- or vibratory-impact
ham-mers operating at high frequency to drive rods into the
sampling interval Reaction force can be reduced if impact
hammers are employed Multipurpose driving systems such as
those commonly deployed for soil gas sampling (Guide
D5314) are frequently used in shallow explorations Some
vibratory drilling systems can provide vibration to the rods and
easily penetrate cohesionless soils On soft ground sites, cone
penetrometer systems use hydraulic rams to push the sampler
and riser pipe into the ground Conventional rotary drilling rigs
can use either hydraulic pull-down capability or hammers to
drive the sampler to the required depth Rotary drilling rigs are
often used with the incremental drilling and sampling method
A140-lb SPT hammer (Test Method D1586) is available on
most rotary drilling rigs and can be used to advance the
sampler Use of impact or vibration may allow for penetration
of harder soils If a significant length of rods whip during
driving, they should be restrained to prevent damaging of the
annular seal at the base of a borehole from lateral movement
7 Conditioning
7.1 Decontamination—Sampling equipment that contacts
groundwater to be sampled before and after the sampling event may require decontamination Decontamination should be performed following the procedures outlined in Practices
D5088and the site-sampling plan The sampler body normally requires complete decontamination before sampling Well-screen components are sometimes expendable Newly manu-factured screens and sampler components may contain residues from manufacture and should be cleaned before the sampling event Riser pipes should be decontaminated if sampling will
be performed within the tube In many cases it’s advantageous
to have several samplers on hand so one can be cleaned while the other is being used
7.2 Purging—For exposed-screen sampling devices and
sampling systems open to overlying groundwater, purging may
be required before the sampling event With both protected-and exposed-screen samplers, purging may be required if groundwater from overlying sources infiltrates into the riser pipes into the sampling area Purging should consist of removal
of overlying groundwater from the sampling system prior to the sampling event Purging requirements are outlined in Guides D6452andD6771
FIG 6 Double-Tube Temporary Well Point System ( 12 ) FIG 7 Protected Screen Sampler with Sample Tubing ( 12 )